Press L1 + L2 + R1 + R2 on the options menu. Note, that dying twice on Normal unlocks Beginner Difficulty which can only be found on the Extra Option menu.

Finish the game to access the secret costume passcode screen. Enter the passcodes to unlock a new costume for Heather.
HappyBirthday (Heather Shirt)
I_Love_You (Onsen)
PutHere2FeelJoy (Block Head)
TOUCH_MY_HEART (Don't Touch)
GangsterGirl (God Of Thunder)
LightToFuture (The Light)
ShogyouMujou (Transience)
BlueRobbieWin (Killer Rabbit)
01_03_08_11_12 (Royal Flush)
cockadooodledoo (Golden Rooster)
PrincessHeart (Transform)
Shut_your_mouth (Zipper)

Beat the game then highlight New Game (Extra) and enter the old Konami code (press UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, CIRCLE, CROSS). Select your difficulties and a sound will verify the code. Douglas will be sans pants when you see him through the game.